The present invention relates to the cutting of materials and, in particular, to cutting tools.
When cutting different materials, for example wood, by means of cutting tools capable of sawing, planing, and milling, etc., it has been possible to facilitate the cutting work and increase production by heating the material.
The cost for heating will be dependent to some extent on the needed temperature increase and, as a rule, to even a greater extent on the size of the workpiece. Usually, the larger workpieces are to be heated to facilitate cutting of one single cut through the piece. Further, this heating is done by time-consuming convection and conduction. As a result, it is only for certain special purposes that the heating technique has been suitable for applications such as veneer lathing, for example. Here, heating is necessary so that the wood can be cut and at the same time, the total heating will be well utilized. The larger part of the whole-heated woodmass will then be cut. Another purpose for the heating technique is the sawing of frozen wood.
According to the invention, an effective heating of only the actual area being cut is achieved. The heating is carried out by electric means and is confined at the cutting wedge tip and influences only the small part of the material (wood) that will be cut. On other large parts of the material which shall not be worked on, no energy is wasted.
The saw blade or the circular saw is preferably made of two parts with insulation therebetween. The saw blades are connected to an electrical voltage so that between the wedges, or between them and a third electrode, a heavy field strength is created, resulting in a strong local heating of the workpiece in the vicinity of the wedge-tips.
The saw can be of a conventional type with fixed teeth or ones which are mutually movable as described in Swedish Patent Application No. 7905412-8. The invention can also be applied to knives which are spread apart and insulation is arranged between the parted units. In the case where there are two knife-blades as described in Swedish Pat. Nos. 313,429 and 324,326, the insulation is applied between the knives. If the material in the workpiece has a high electrical conductivity, for example metal, the heating current is produced by ohmic resistance, from a suitable DC-source or AC-source with low frequency. When working on material with low conductivity, for example wood, plastics, etc., the energy is applied dielectrically with high frequency. The heat is concentrated in the cutting area of the material partly due to the sharp wedges and partly because the distance between electrically cooperating teeth is short. Areas with a greater distance from the wedges thus will not be even slightly heated.
The fronts of the teeth are preferably formed in the same manner as described in the above-mentioned Swedish Patent Application No. 7905412-8. The saw blades shall have equal tooth-pitch and the teeth in the saw blades shall have front faces or edges so oriented that the blades are pressed together by shear forces. This is achieved in that the teeth in the left blade (seen in the sawing direction) has a front directed towards and acting to the right at the grip in the wood and that the teeth in the right blade has a front directed to and acting to the left at the grip in the wood.
The active cutting tools thus can steer the cut to the right or the left. A similar steering effect can be achieved by the present invention by an appropriate distribution of the heating of the saw cut so as to facilitate cutting by one or the other of the blades. This is done by introducing a third electrical system and a varied voltage feeding to the two saw blades. The afore-mentioned right/left forces are influenced by the above-mentioned electrical voltage feeding due to the changed cutting resistance created by the heating.